Inertial flow of a dilute suspension over cavities in a microchannel

Microfluidic experiments and discrete particle simulations using the lattice-Boltzmann method are used to study interactions of finite size hard spheres and vortical flow inside confined cavities in a microchannel. The work focuses on entrapment of particles inside confined cavities and particle dynamics after entrapment. Numerical simulations and imaging of fluorescent tracers demonstrate that spiralling flow generates exchange of fluid mass between the vortical flow and the channel, contrary to the concept of a well-defined separatrix in unconfined cavities. An isolated finite size particle entrapped in the cavity migrates towards a stable orbit, i.e. a limit cycle trajectory. The topology of the limit cycle depends on cavity size, particle diameter and flow inertia, represented by Reynolds number. By studying various factors affecting the acceleration of a particle before entrapment, it is discussed that entrapment is a collective effect of flow morphology and particle dynamics. The effect of hydrodynamic interaction between particles inside the cavity, which results in deviation from the stable limit cycle orbit and depletion of cavities, will also be discussed. It is shown that a wall-confined microcavity entraps particles based on particle size, therefore it provides a platform for microfiltration.